Believe it or not, people aren’t totally transparent to one another. Liars can seem honest, spies can seem loyal, nervous people can seem guilty. People’s facial expressions are not a reliable guide to what they are thinking. Or, to put it in Hamlet’s words, one may smile, and smile, and be a villain. Makes you think, doesn’t it?

If any of this is surprising to you, then you are in exalted company, because it also surprises Malcolm Gladwell, whose job it is to be puzzled by banalities and then replace them, after a great pseudo-intellectual circumambulation, with banalities. Gladwell affects to find it baffling how we can get people we don’t know so wrong. So he calls it “the stranger problem”, and pretends that it explains everything.

It explains, for example, the fate of a young black woman named Sandra Bland. Gladwell introduces her by remarking that she was “tall and striking, with a personality to match”, which is just the kind of deft pen-portrait that has earned him a reputation as a brilliant writer for the best magazines. In Texas in 2015, Bland was pulled over for a traffic infraction by a cop named Brian Encinia. The encounter rapidly degenerated as the hostile and suspicious state trooper forced her out of the car, called for backup, and had her arrested. Days later Bland was found dead in her cell.

You will guess that there is a counterintuitive take coming: Gladwell wants us to feel sorry for the cop. “Think about how hard it was” for him, he pleads. “Sandra Bland was not someone Brian Encinia knew from the neighborhood or down the street ... They were strangers to each other.” Other policemen stop strangers all the time without bullying them and hauling them in, but never mind that now. Encinia, as Gladwell credulously interprets his subsequent statements, was “terrified” of this young woman, who might after all have been planning to burn him with her cigarette. It’s very difficult, don’t you see, not to be a brute.

What else is it difficult not to be? In Gladwell’s world of large ideas, it may also be hard not to be a rapist when you’re drunk. He brings his forensic empathy to the case of Brock Turner, the Stanford college student who was caught sexually assaulting an unconscious woman on the ground outside a dorm building. Such a difficult case! Gladwell explains sorrowfully that consuming large amounts of alcohol causes mental “myopia”, where one is unable to consider the long-term consequences of one’s actions. It’s just too bad, he concludes, that these careless students both got so drunk at a party that the man could “tragically misunderstand” the woman’s intentions. You may object that plenty of men are able to get blattered without raping anyone, but that seems to be beyond Malcolm Gladwell.

To be sure, this book is not exclusively about standing up for the unlucky men who accidentally do bad things just because the “stranger problem” is so lamentably intractable. It is also littered with historical and pop-cultural anecdotes. Why did Chamberlain think Hitler sincerely wanted peace? Such a “puzzle” leads us through stories about Cuban espionage, predatory paedophiles, the Bernie Madoff fraud, Sylvia Plath’s suicide, the interrogation of Khalid Sheikh Mohammed, and the TV show Friends. “Maybe real life isn’t like Friends,” Gladwell suggests, momentously.

Gladwell bases his book on a single notion called “truth-default theory”. We tend to assume that other people are telling the truth, which is the basis of trust and social cooperation, so liars are hard to spot. Not mentioned here is the well-known opposite phenomenon: that, far from defaulting to truth, we believe only the information that fits with our preconceived biases. Both ideas are right, because the world is complicated, but Gladwell’s job is to make it seem simple.

Another teachable story here is that of Amanda Knox, the American student in Perugia who was imprisoned for murder (and later acquitted) because her behaviour after the crime seemed extremely odd. Gladwell assures us that weird behaviour is not reliable evidence of guilt. There is a psychological phenomenon called “the illusion of asymmetric insight”: we consider ourselves opaque to others, while thinking that other people are easy to read correctly. “If I can convince you of one thing in this book,” he announces dramatically, “let it be this: Strangers are not easy.”

Perhaps if we can all become convinced of this novel truth, we will stop harassing and raping one another for good. If only someone like Shakespeare had encoded the lesson centuries ago in some memorable form, like, I don’t know, “There’s no art / To find the mind’s construction in the face.” In the absence of such poetic conventional wisdom, though, another book by Gladwell just might save the world.

• Talking to Strangers: What We Should Know about the People We Don’t Know is published by Allen Lane (£30). To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.